Now the word came from the XDA-Developers Forums that the Froyo ROM from myTouch 3G is ported to the T-Mobile G1. According to this report, Android 2.2 works all well and fine on the G1 and this just shows what a brilliant handset this one is.
To get the Froyo treatment for your G1, your device has to be rooted, along with two other requirements – your T-Mobile G1 to have the 1.33.2005 dangers SPL and 2.22 radio. For more information visit the XDA through the link below.
Source: XDA-Developers via Android Guys